The present invention relates generally to processes, procedures and equipment for the preparation of food product as well as the storage and handling of food product after it has been prepared.
Numerous preparation devices and procedures are known to be useful in the preparation of foods including several types of ovens and similar equipment.
For example, such food processing equipment includes dry ovens which are commonly known and in wide use. Dry ovens generally have a chamber which is heated by various means and is provided with control means to maintain the temperature in the chamber within selected limits.
In the use of dry ovens it is not generally recognized that processing food in dry ovens causes water vapor to continually enter and leave the food in preparation. Furthermore, no prior art procedure is known which recognizes that there is an equilibrium water activity specific to each food where water vapor enters and leaves the food product at the same rate so that there is no overall loss or gain of water content in the food product. Most foods in general have equilibrium water activities in the range of 0.2 to 1.0.
Specifically, prior an processes and apparatus have not recognized the benefits achieved from the use of equilibrium water characteristics of food products in the preparation of the food.
In addition to dry ovens, the prior art includes other equipment such as steamers where the cooking chamber is from time to time saturated with water vapor; but again without recognition of the equilibrium water activity of the food product in preparation.
Some prior art procedures and apparatus have attempted to combine the effects of the dry oven and steamers by periodical injection of water vapor into the food processing chamber. In general, such prior art apparatus and procedures have maintained the air temperature in the chamber at selected levels and injected water vapor as water or steam to maintain moisture content in the enclosure, again without consideration of the equilibrium water activity of the food being processed. Again, the prior art does not recognize the unexpected benefits of adjusting moisture characteristics in the oven in relation to the equilibrium water activity of the food being processed to effect desired results in the food product. Further, the moisture and temperature characteristics may be selectively adjusted during the processing of the food product to achieve desired final characteristics of the food product.
In this regard no prior art apparatus or procedure is known where water is introduced to the chamber by any method so that the moisture content is maintained in relation to the equilibrium water activity of the food product and further where the vapor content of the air in the chamber can be adjusted relative to the equilibrium water activity of the food being processed to achieve desired final characteristics of the food product.
In fact, in many prior art arrangements, the expansion realized by injection of water vapor causes the vapor to condense. Since the food product usually presents the coolest surface area in the chamber the vapor condenses on the food and undesirably wets the surface of the food. As a result, the quality of food prepared in such devices suffers unless a great deal of attention is devoted to the operation of the device.
Further with respect to "dry" ovens, the loss of water content which occurs in preparation of some foods leads to the general conclusion that food prepared in a dry oven is ". . . dry, hard, tough, tasteless, . . . stale . . . . " Additionally, some foods prepared in a dry oven are likely to evidence shrinkage because of the moisture loss during processing. It is such loss of moisture which also leads to shrinkage of the food and deterioration of appearance.
It is recognized that in the preparation of foods in a dry oven there may be a very narrow time window during which the food is cooked to the desired degree and characteristics. If the food is not removed from the oven at this time deterioration of the food begins. As a result the watchful care of a skilled chef is generally necessary to achive the best results. Even then it is not possible to maintain the food product in the oven past the optimum time without deterioration of the food.
Additionally, dry ovens are inherently not energy efficient.
Specifically, the operating cost of dry ovens is increased because of the excess heat needed to compensate for the substantial loss of moisture from the food in preparation. In operation of dry ovens, heat is transferred to the food principally by convective heat transfer to the air in the chamber followed by convective heat transfer from the air to the food. Since the air in a dry oven is generally dry, and the specific heat of dry air is lower than the specific heat of moist air, then the rate of heat transfer from the air to the food is lower for dry air and preparation times are correspondingly extended. Also because of the lower specific heat of dry air, the temperature of the heat transfer surfaces used to transfer heat to the air must be increased. Because of the increased temperature required and the extended time required for processing the food, additional energy is required over that which would be used if the moisture content of the air were increased.
Processing time and energy loss is further extended by the energy required for the unnecessary evaporation of water from the food being processed. This evaporation process also extends the processing time required for preparation of the food.
Another problem commonly encountered with conventional ovens is air leakage from the oven, usually through the door gasket. In dry ovens the quality and time of food preparation is directly affected by loss of air and heat from the oven. Specifically, heated air lost from the oven must be replaced, and compensation for lost air even further aggravates the conditions described above. Additionally, air lost from dry ovens removes moisture from the oven which is compensated for by further evaporation of water from the food being processed and leads to even further deterioration of the food.
The prior art has further provided forced convection within a dry oven in an attempt to improve heat transfer. The use of forced convection fails to recognize the effects of equilibrium water activity and further accelerates drying of the food product during preparation.
Some other prior art arrangements have used steam to maintain a given humidity in the cooking chamber. However, such arrangements fail to realize that maintaining a designated relative humidity in the cooking chamber does not alleviate the aforenoted deficiencies. For example, if the relative humidity is maintained at a value above the equilibrium water activity of the food being processed then the food will gain moisture with the likelihood that the food product will become "soggy". Alternatively, if the humidity is maintained at a value much below the equilibrium water activity of the food, the above effects will be noted. Further, the maintenance of uniform relative humidity throughout the entire preparation cycle does not recognize the advantages realized by preparation of the food at conditions below, equal to, and above the equilibrium water activity of the food at various times during the processing cycle.